The present invention relates generally to an image sensor, and more particularly, to a photo detector device capable of detecting an image input from a stylus, pen, torch or a shadow.
With the rapid development in the high-tech industry, pen tablets have been widely applicable to Personal Digital Assistants (PDAs), Personal Computers (PCs) and other electrical appliances used in our daily life. Generally, a pen tablet includes one of a resistor-type, electromagnetic inductance-type, capacitor-type and optoelectronic-type writing panel. As an example of a conventional optoelectronic-type pen tablet, an optical signal may be converted into electrical charges, which in turn may be stored in a capacitor of a detector array including capacitors, optoelectronic components and switch transistors before it is subsequently read. The capacitors may require additional areas and therefore adversely reduce the aperture ratio of the panel. Furthermore, the charges generated by a background light source and an input signal may be stored in the capacitor, adversely resulting in a relatively narrow dynamic range. It may therefore be desirable to have a photo detector device that is able to convert an optical signal into a photocurrent, thereby eliminating the storing capacitors used in the conventional panels. It may also be desirable to have a photo detector device of which the photosensitive transistors and associated circuits may be fabricated simultaneously with the thin film transistors of a liquid crystal display (LCD) device.